Coating of thermionic cathodes



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June 8, 1943'. 5. J. KOCH 2,321,149.

COATING OF THERMIONIC CATHODES Filed Aug. 28. 1 941 Y FITTQRNEY INVENTOR.

Patented June 8, 1943 2,321,149 COATllNG F THEBlGNIC' CATHODES Stanley J. Koch, Clifton,

B. Du Mont Laboratories, Inc., Passaic, N. 3., a corporation of Delaware Application August 28.1941, Serial No. 408,635

7 Claims.

This invention relates to thermionic cathodes.

- It relates. more particularly to cathodes of the type that are to beused in cathode-ray tubes where a metal cathode is used and coated with material that has the characteristic of emitting electrons at a high rate when heated.

Heretofore, when tubes have been-coated with electron emissive materials to increase the electron emission, the coatings have been so applied that troubles have arisen due to the fact that the coatings have not been confined tothe areas where it is desired that they should be located, but accidentally adhere to other surfaces.

By the present invention, cathodes are coated very rapidly and safely with electron-emitting material in such a manner that the material'is applied to areas where the coating is desired, with the result that the cathodes operate more satisfactorily. Also, when such cathodes are used in electron-ray tubes, they can be located accurately with respect to the gun elements such as the control grid, resulting in better performance.

In carrying out this invention a large number of cathodes that are to be coated with electronemissive material may be placed in position and the desired predetermined portions quickly coated while the cathodes are assembled without accidentally coating other portions thereof.

The invention will be understood from the descrlption in connection with the accompanying drawing, in which: v

Fig. 1 is a plan view of a plate used in coating a plurality of cathodes at one time;

Fig. 2 is a section on an enlarged scale along the line 2-2 of Fig. 1 showing a portion of the plate and one of the cathodes in place to be coated; and

Fig. 3 shows how one of the coated cathodes can be accurately located with respect to a control grid.

In the drawing, reference character I- indicates a plate which may be of metal having a number of holes 2 and bolt holes 3 therethrough. A thin plate 4, of springy metal with smaller holes 5 concentric with the holes 2 and with holes 6 concentric with the holes 3, is slightly bent or cupped so that its central portion will first strike any flat surface upon which it is laid.

A cathode I, which may be made of metal such as nickel, for example, is provided with a heater 9, of tungsten, for example, that may be insulated with ceramic insulation in the well known way. A cap 9 is provided for the cathode I, and has a flange lli'by means of which the cap is securely attached to the cathode. The cap 9 is provided N. 3., assignor to Allen on its outer side with a pan-shaped or central depressed portion ii to which the electron-emissive material i2 is to be applied.

A thick. plate I3 (Fig. 2) is provided with holes id equal in number to the holes 2 or 4 to accommodate cathodes I, and with countersunk holes i5, to accommodate the flanges l0 and provide ledges it upon which the edges of these flanges rest to support the cathodes 1 accurately and securely in place. The plate I3 is also provided with holes I! aligned with the bolt holes 3 and 6 in the plates i and d to accommodate the bolts the edges of the flanges I8 having nuts iii.

In applying the electron-emissive material to the cathodes l, a number of rows of the cathodes are assembled with several cathodes in each row in any convenient way so that the number of cathodes equals the plate I. The cathodes are assembled in an up-v right position in the holes 14 of the plate l3 with ill of the caps 9 resting upon the ledges IS. The plates i and I are placed upon these cathodes alignment with the cathodes, the bolts I are inserted and the nuts tightened. The electronemissive material, mixed with any suitable binder,

is then sprayed upon the plate I, whereupon the material passes through the holes 2 and 5 and enters the pan-shaped central portions 9 of the cathodes until the same have been fllledsufliciently. In this way the electron-emissive material is applied uniformly to each cathode in the 'form of discs without any of this material accidentally coating any undesired portion of. the cap 8 such as the rim l0.

In Fig. 3 is shown an advantage of applying the electron-emissive materials in accordance with this invention. In this figure, reference character 22 indicates a grid control for a cathoderay tube having an aperture 23 for the electron beam in the end 24 of the grid control. A pair of openings 25 is provided diametrically opposite each other through the grid control 22 adjacent the end 24. A spacing bar 26 of a thickness equal to the desired distance from the rim of the cap 8 i to the end 24 of the grid control 22 is shown extending through diametrical holes 25 in the grid 22. The cathode l is inserted into the control grid 22 until the rim of the cap 9 contacts with the spacing bar 26. The grid 22 andcathode' 1 g are then fixed in position with respect to each other in the known way and the spacing bar '26 is then removed. 1

Among the advantages of having the'electronemissive material properly applied without irregnumber of holes 2 in thewith the holes 5 and 2' in s ular spots around are that the electron-emissive material can be properly located with respect; to the apertures 23 01' the control grids; and also, by means odes can be located at the exact desired position from the apertures 23, as no portion or the electron-emissive material would accidentally lodge upon the rim of the cap 9 and cause a variation in the position in which the cathodes 1 are located by means or the spacing bar 26 with respect to the apertures 23. I

What is claimed is:

l. The method or coating the end of a cathode, which comprises locating the end of said cathode in a circular recess in the upper surface or the spacing bar 2 each 01' the cathof a thick plate, said recess being coaxial with a hole of smaller diameter through said plate,

and applying coating material to said cathode in a downwarddirection through a hole of smaller diameter in another plate.

2. The method or coating the end of a cathode, which comprises locating the end of said cathode in a recess around a hole in a plate, and applying coating material to it in a downward direction through a hole in another plate while shielding the rim of said end from the coating material.

3. The method of coating the end of a cathode, which comprises locating a cathode having a depression in the end thereof in a recess around a hole in a plate, and applying coating material to said depression through a hole in another plate 'while confining the outer surface area of said coating on said cathode below the upper edge of the depressed area oi said depression.

.ing material to it in 4. The method or coating the end 01' a cath- Ode having a central depression in said end, which'comprises locating the end or said cathode in a circular recess in the upper surface oi a thick plate, said recess being coaxial with a hole of smaller diameter through said plate, and applying coating material to said cathode in a downward direction through a hole 01' smaller diameter in another plate. ,7 5. The method of coating the end or a cathode having a central depression in said end, which end oi said cathode in a recess around a hole in a plate, applying coating material to it in a downward direction through a hole in another plate, and confining said coating material to said depression.

6. The method-or coating the end 01' a cathode having a central depression in said end, which comprises locating the end of said cathode in a recess around a hole in a plate, applying coata downward. direction through a, hole in another plate, confining said coating material to said depression, and preventing it from reaching the rim around said depression.

'7. The method having a central of coating the end oi. a cathode .depression in said end, which comprises locating the end of said cathode in arecess around a hole in a plate,-spraying coating material upon it in a downward direction through a hole in another plate, confining said coating material to said depression, and preventing it from reaching the rim around said depression.

STANLEY J. KOCH. 

